Generally, an inverter is an inverse conversion device that electrically converts DC to AC. An inverter used in the industry is defined as a series of devices that control a motor speed such that the motor is used with a high efficiency by receiving a power supplied from a commercial power supply and varying a voltage and frequency of the power by itself and supplying the varied power to the motor. The inverter is controlled via a variable voltage variable frequency (VVVF) scheme. The inverter may vary a voltage and frequency input to the motor based on a pulse width modulation (PWM) output.
A slip frequency of the motor is defined as a difference between a rotational speed of the motor and a rotating field generated by the inverter. When the slip frequency of the motor increases greatly, overcurrent will occur and thus the inverter or motor will be damaged. To prevent this damage, when the overcurrent occurs, the inverter may suppress the overcurrent or generate a trip signal to protect the inverter and motor.
When the overcurrent protection operation is performed to protect the inverter from the overcurrent, a peak value of the output current of the inverter (hereinafter, a peak-current) may be detected.
Conventionally, there may occur a period in which the detection of the peak current is not available based on the output current state of the inverter. Thus, even when a current level exceeds the overcurrent level, the overcurrent suppression may not be realized in the period. Thus, there arises a problem that internal elements of the inverter may be damaged due to the overcurrent and a trip may occur due to overheating.